Absence of Mutagenic Effects of 3- and 6-Alkyl-5-bromouracil Herbicides on a Bacteriophage

Abstract

SINCE the 1962 report by Bucha et al.¹, who described the herbicidal activity of certain uracils substituted in the 3 and 6 positions, one of this class of chemicals, 5-bromo-3-sec-butyl-6-methyluracil (bromacil), has gained wide acceptance as an industrial herbicide. Investigations of the mode of action of this herbicide^2,3 have shown that it is a potent direct inhibitor of photosynthesis acting at the chloroplast level. The chemical analogy between 5-bromouracil and the foregoing 3,6-substituted 5-bromouracil suggested the possibility that it might be incorporated into DNA and thereby act as a mutagen. McGahen and Hoffmann^4,5 were unable to demonstrate incorporation of 5-bromo-3-sec-butyl-6-methyluracil (IV) either into the DNA of a thymineless Escherichia coli (15T−) or into mouse liver DNA under conditions in which 5-bromouracil (5-BU) was incorporated. Their investigations, however, did not rule out the possibility of indirect mutagenic activity. The subject of this report is a comparison of the effects of 5-BU and 5-bromouracils with several different alkyl substituents at the 3 and/or 6 positions on the back-mutation of an aminopurine-induced rII mutant of coliphage T4.